The anatomical connections of the auditory cortex are indicative of its role in the function of the nervous system. Differences in connections among segments of the auditory cortex imply differences in anatomical organization and function. The proposed project is directed toward elucidating the organization of the primate auditory cortex by: 1) detecting differences in the distribution of cortical efferents from areas responsive to auditory stimulation, 2) analyzing such areas cytoarchitecturally, 3) defining the primary auditory area and 4) determining the synaptic organization of a selected receptive layer. The distribution of the cortical efferents and geniculocortical fibers will be traced with reduced silver methods (Nauta-Gygax and Fink-Heimer) by following the degeneration resulting from stereotactic lesions placed in the auditory responsive cortex and medial geniculate body. Nissl preparations will be utilized to describe the cytoarchitecture of segments of the auditory responsive cortex. The synaptic organization of selected layers in the primary auditory cortex will be determined by electron microscopy of degenerating terminals.